SCHOTT solutions no. 2/2012 > Nanostructuring

SCHOTT developers have further improved the nanoimprinting process. Now it can even be used to produce hologramson glass surfaces. Photo: SCHOTT/C. Costard

Guiding Light with Precision

SCHOTT developers are creating nanostructures on glass surfaces and transforming nanoimprint techno-logy into a platform for creating innovative products and applications.

Thilo Horvatitsch

Under the lens of an electron microscope, they form a landscape of mysterious identical sculptures: periodically arranged silicon crystals on a glass surface. Engineers can specify their exact size, shape, and spacing down to the micrometer and nanometer. To allow even greater precision, SCHOTT developers have refined a process for nanostructuring surfaces that is one of today’s most important emerging technologies: nanoimprint lithography.

Using this nanoimprint technology in combination with special coating materials and processes, developers can create complex functional surface structures. These structures are so small and sophisticated that they can direct, reflect, absorb, or manipulate incident light. This technology can also be used to generate surfaces with specific haptics or decorative flair.

The production process includes a curing step with ultraviolet light. Photo: SCHOTT/C. Costard

”We want to take advantage of these new opportunities and are working hard to turn nanostructuring into a technology platform for the future development of innovative applications and products,” says Dr. Eveline Rudigier-Voigt, SCHOTT Senior Manager on Coatings. Progress has been made: the nanoimprint process has already been refined in several ways. This technology was previously confined to industrial settings and relatively large surfaces and usable only with flexible substrates, primarily plastics. Rigid materials such as glass allowed only small-scale structuring – nanostructured wafers or diffractive optical elements (DOEs), for example, as the successors to traditional lenses and mirrors. In addition, conventional processes are very slow, require many process steps, or are not suitable for large surfaces or rigid substrates such as special glass. By contrast, an initial technological prototype from SCHOTT permits not only glass nanostructuring, but also rapid production of 30 cm x 40 cm glass formats.

SCHOTT has also applied the principles of chemical nanotechnology to develop a special sol-gel based nanoimprint coating. Applied to a glass substrate, this coating accommodates a wide variety of features, such as a customized refractive index for optical applications.

A stamp is produced to manufacture an optical interference screen for diffracting light (left). SCHOTT also employs this technique to produce a realistic brushed stainless steel look on glass (right). Photo: SCHOTT/C. Costard

Furthermore, these structures are very temperature-resistant. Even without considering the naturally heat-resistant glass substrate, the coatings developed or used in such cases can handle temperatures of over 200 to 700 degrees Celsius. Highly temperature resistant vitreous sol-gel coatings suitable for use in hot operation areas can also be created.

”This technology platform opens the doors to a wide variety of possible applications. We have secured broad patent protection for our materials and processes that will cover numerous applications,” comments Dr. Matthias Bockmeyer, SCHOTT Senior Manager on Material Development. Other possible applications include architectural glass with special anti-reflective surfaces, holograms for product trademark protection, and optical nanostructures for light emission on OLEDs (organic light-emitting diodes). Diffusion filters to distribute light more evenly on video screens are another option. Also, optical ”light-trapping” concepts for more efficient absorption of light by the nanostructured substrate could be an interesting application for thin-film solar technology.

At SCHOTT, developers are already working on a decorative application for household appliances: the creation of a realistic brushed stainless steel look on glass. This allows the advantages of glass, such as easy cleaning and scratch resistance, to be combined with the elegant, stylish look of metal. Furthermore, nanoimprint technology allows many different colors and shapes to be used on glass surfaces.

The periodically arranged, wavelength-ordered crystalline silicon structures mentioned at the beginning of this article, which are being developed in a joint project with the Helmholtz Center in Berlin, could be an important future field of endeavor for SCHOTT. One of the primary project goals is the low-cost production of photonic crystals for the controlled manipulation of light propagation in a material and/or how light interacts with it. This should significantly boost (optical) data processing power – a prerequisite for the optical supercomputer of the future. <|

Left: Periodically arranged silicon crystals on a glass surface. Their shape, size and the distances in between them can be determined down to the nanometer. Right: Coating, embossing, hardening and treating: The basic process of nanoimprint lithography is quite simple and yet challenging.

There are many different processes available for surface microstructuring and nanostructuring, including milling, laser cutting, hot forming, or lithographic processes. However, with nanoimprint lithography, an embossing rather than a photolithographic process is used to do the structuring. In the basic process, a stamp (negative) forms nanostructures in specially coated materials (positive), which are then exposed to UV light or thermally cured. The technology is known for its extreme precision into the low nanometer range as well as its potentially high surface throughput, which allows for inexpensive mass production. The advanced nanoimprint lithography process from SCHOTT can create structures stretching into the micrometer-to-nanometer range – equivalent to one-billionth of a meter. Developers have also applied the principles of chemical nanotechnology to create a special sol-gel varnish that is applied to the glass substrate. A flexible stamp presses the nanostructure into this layer, and then a thermal treatment is applied to harden the material.

SCHOTT developers are using nanostructured substrates to research and test innovative products such as cost-efficient photonic components. The unique and long-standing expertise in specialized glass and sol-gel coatings that SCHOTT possesses is being combined with other processes such as electron beam evaporation, solid phase crystallization, and wet chemical etching. <|